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Engineering Science 1021A/B Lecture Notes - Lecture 11: Relative Atomic Mass, Activation Energy

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scarlethound445
17 May 2018
School
Western University
Department
Engineering Science
Course
Engineering Science 1021A/B
Professor
Anita Woods

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Simplest forms of point defects are vacancies and self-interstitials
○
•
•
Vacancy: atom is missing from its normal site in the crystal structure
•
Number of vacancies found in a material is dependent on temperature
Concentration of vacancies increases exponentially as temperature increases
!"# $ % &'()*
+, -
!: number of possible sites for a vacancy
Total number of atoms
®
□
.": activation energy for vacancy formation□
/: Boltzmann's constant
0123405(67 8
9:;<%=
®
□
> # absolute temp in K□
§
○
•
Self-Interstitial: extra atom is inserted into the crystal structure at a normally unoccupied
position
•
All metals contain some level of impurities•
Solid Solution
When one element is added to another, an alloy is formed•
One of the potential ways in which the atoms can mix•
In solid solutions, solute atoms form point defects in the solvent•
Defects can be interstitial or substitutional depending on the relative size of the atoms
○
○
•
Solid Solution Strengthening
Intentionally creating point defects by alloying one metal with another element can be
used to increase the strength
•
If the solute atoms have a different radius than the matrix, then the lattice will be
distorted
The stress field around the solute atom will interact with the stress field around the
dislocation
○
It will be more difficult for the dislocation to pass the solute atom
○
Tensile lattice strains imposed on host atoms by a smaller substantial impurity
atom
(a)
Possible locations of smaller impurity atoms relative to an edge dislocations
such that there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
Compressive strains imposed on host atoms by a larger substantial impurity
atom
(a)
Possible locations of larger impurity relative to an edge dislocation such that
there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
•
A material is strengthened when it is made more difficult for dislocations to move•
A large difference in solute/matrix size creates a stronger distortion in the lattice and
makes it more difficult for a dislocation to pass
○
•
Alloy Composition
The composition of an alloy can be expressed as:
Weight %
§
○
Atom %
§
○
•
Conversion between atomic and weight % requires:
Atomic weight
○
Density
○
Avogadro's #
○
•
Point Defects
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Simplest forms of point defects are vacancies and self-interstitials
○
•
•
Vacancy: atom is missing from its normal site in the crystal structure
•
Number of vacancies found in a material is dependent on temperature
Concentration of vacancies increases exponentially as temperature increases
!"# $ % &'()*
+, -
!: number of possible sites for a vacancy
Total number of atoms
®
□
.": activation energy for vacancy formation□
/: Boltzmann's constant
0123405(67 8
9:;<%=
®
□
> # absolute temp in K□
§
○
•
Self-Interstitial: extra atom is inserted into the crystal structure at a normally unoccupied
position
•
All metals contain some level of impurities•
Solid Solution
When one element is added to another, an alloy is formed•
One of the potential ways in which the atoms can mix•
In solid solutions, solute atoms form point defects in the solvent•
Defects can be interstitial or substitutional depending on the relative size of the atoms
○
○
•
Solid Solution Strengthening
Intentionally creating point defects by alloying one metal with another element can be
used to increase the strength
•
If the solute atoms have a different radius than the matrix, then the lattice will be
distorted
The stress field around the solute atom will interact with the stress field around the
dislocation
○
It will be more difficult for the dislocation to pass the solute atom
○
Tensile lattice strains imposed on host atoms by a smaller substantial impurity
atom
(a)
Possible locations of smaller impurity atoms relative to an edge dislocations
such that there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
Compressive strains imposed on host atoms by a larger substantial impurity
atom
(a)
Possible locations of larger impurity relative to an edge dislocation such that
there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
•
A material is strengthened when it is made more difficult for dislocations to move•
A large difference in solute/matrix size creates a stronger distortion in the lattice and
makes it more difficult for a dislocation to pass
○
•
Alloy Composition
The composition of an alloy can be expressed as:
Weight %
§
○
Atom %
§
○
•
Conversion between atomic and weight % requires:
Atomic weight
○
Density
○
Avogadro's #
○
•
Point Defects
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 10 pages and 3 million more documents.

Already have an account? Log in
Simplest forms of point defects are vacancies and self-interstitials
○
•
•
Vacancy: atom is missing from its normal site in the crystal structure•
Number of vacancies found in a material is dependent on temperature
!"# $ % &'()*
+, -
!
: number of possible sites for a vacancy
Total number of atoms
®
□
."
: activation energy for vacancy formation
□
/
: Boltzmann's constant
0123405(67 8
9:;<%=
®
□
> #
absolute temp in K
□
§
○
•
Self-Interstitial: extra atom is inserted into the crystal structure at a normally unoccupied
position
•
All metals contain some level of impurities
•
Solid Solution
When one element is added to another, an alloy is formed
•
One of the potential ways in which the atoms can mix
•
In solid solutions, solute atoms form point defects in the solvent
•
Defects can be interstitial or substitutional depending on the relative size of the atoms
○
○
•
Solid Solution Strengthening
Intentionally creating point defects by alloying one metal with another element can be
used to increase the strength
•
If the solute atoms have a different radius than the matrix, then the lattice will be
distorted
The stress field around the solute atom will interact with the stress field around the
dislocation
○
It will be more difficult for the dislocation to pass the solute atom
○
Tensile lattice strains imposed on host atoms by a smaller substantial impurity
atom
(a)
Possible locations of smaller impurity atoms relative to an edge dislocations
such that there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
Compressive strains imposed on host atoms by a larger substantial impurity
atom
(a)
Possible locations of larger impurity relative to an edge dislocation such that
there is partial cancellation of impurity
Dislocation lattice strains□
(b)
○
•
A material is strengthened when it is made more difficult for dislocations to move•
A large difference in solute/matrix size creates a stronger distortion in the lattice and
makes it more difficult for a dislocation to pass
○
•
Alloy Composition
The composition of an alloy can be expressed as:
Weight %
§
○
Atom %
§
○
•
Conversion between atomic and weight % requires:
Atomic weight
○
Density
○
Avogadro's #
○
•
Point Defects
Unlock document

This preview shows pages 1-3 of the document.
Unlock all 10 pages and 3 million more documents.

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Document Summary

Simplest forms of point defects are vacancies and self-interstitials. Vacancy: atom is missing from its normal site in the crystal structure. Number of vacancies found in a material is dependent on temperature. Concentration of vacancies increases exponentially as temperature increases. : number of possible sites for a vacancy. Self-interstitial: extra atom is inserted into the crystal structure at a normally unoccupied position. When one element is added to another, an alloy is formed. One of the potential ways in which the atoms can mix. In solid solutions, solute atoms form point defects in the solvent. Defects can be interstitial or substitutional depending on the relative size of the atoms pied. Intentionally creating point defects by alloying one metal with another element can be used to increase the strength. If the solute atoms have a different radius than the matrix, then the lattice will be distorted.

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8.
Assume that the variable table holds a two-dimensional list of integers. Write code that computes the sum of all elements in the table, assigning the result to the variable table_sum.